Jet solder feeding devices are already known in which soldering is carried out for a substrate having surface mounted parts and discrete parts (parts with lead legs) consolidated thereon by feeding molten solder ejected from jet nozzles to the substrate while letting the substrate being conveyed.
Jet solder feeding devices of this type include the one which comprises: a first jet nozzle 1 for feeding molten solder satisfactorily to a substrate P mounted with electronic parts in the whole area of the surface to be soldered and a second jet nozzle 2 for removing excess molten solder having been fed to the substrate P, as shown in FIGS. 3 and 4. The first jet nozzle 1 and the second jet nozzle 2 are connected to a duct 3 for the first nozzle and a duct 4 for the second nozzle, respectively, both of which are soaked in molten solder accumulated in a solder melting bath 5. This jet solder feeding device is designed to eject molten solder from the first jet nozzle 1 and the second jet nozzle 2 toward a substrate-conveying path 10 by rotationally driving jet impellers 6 and 7 arranged to face each of the openings at one end of the duct 3 and at one end of the duct 4, respectively.
On the upper end portion of the first jet nozzle 1, a corrugated plate 9 with multiple open ejecting ports 8 is mounted. As shown in FIGS. 5a and 5b, the ejecting ports 8 have the same bore diameter and the same round shape and are provided, for example, in three rows in the direction B perpendicular to the direction A in which the substrate P is conveyed: ejecting ports 8A in an upstream row, ejecting ports 8B in an intermediate row and ejecting ports 8C in a downstream row, and all the ejecting ports 8 are formed in different locations relative to the direction B perpendicular to the direction A in which the substrate P is conveyed. Each of the wall portions surrounding each ejecting port 8 on the corrugated plate 9 is designed to be flat.
The substrate P warps to some degree when heated by the molten solder, and when piles of molten solder ejected from ejecting ports 8A become low, portions are created on the surface of the substrate P or the electronic parts intended to be soldered which the molten solder will not come in contact with. This causes poor wetting.
One of the conventional techniques to possibly deal with this problem is such that the piles of the molten solder are made higher by increasing the number of revolutions of the jet impellers 6 and 7.
In the above described conventional jet solder feeding device, however, although the average height, on a time basis, of the piles of the molten solder becomes higher by increasing the rpm of the jet impellers 6 and 7, the height is very unstable since it varies with time. Accordingly, when the piles of molten solder ejected from ejecting ports 8 temporarily become low, portions may be created on the surface of the substrate P or the electronic parts intended to be soldered which the molten solder will not come in contact with; consequently, poor wetting is caused in some part of the substrate.
There is an alternative in which ejecting pressure is increased by decreasing the bore diameter of each ejecting port 8. In this case, however, since the cross-sectional area of the ejection from each ejecting port 8 becomes smaller, the area of the contact surface of the substrate P also becomes smaller, and there is still a possibility of causing poor wetting.
The present invention has been made to solve the above problem. Accordingly, the object of the present invention is to provide a jet solder feeding device and a method for soldering which make it possible to keep the molten solder ejected from ejecting ports at a desired height in a more stable manner.